The present invention relates to a semiconductor device, and is applicable to a semiconductor device incorporating an electrically rewritable non-volatile memory, such as a flash memory.
Recently, flash memories are widely used as devices which store programs or data. The flash memories are electrically rewritable non-volatile memory units. The flash memories are memory units which can erase/write the storage contents many times, by increasing a voltage to be applied at the time of rewriting higher than a voltage at the time of reading. That is, rewriting is performed by applying a pulse-like voltage to the memory unit, and by controlling a current to flow through a gate insulating film to inject electrons to the memory unit and draw out the electrons.
In this manner, deterioration of the flash memory cannot be avoided in nature, because it is necessary to cause a current to flow through the gate insulating film every time the rewriting is performed. As a result, the flash memory cannot be rewritten as the deterioration of the deterioration of the memory unit progresses. One feature thereof is that there is a limit of the number of rewriting. Thus, it is important to provide a technique for applying an appropriate pulse voltage with an appropriate pulse with, to the memory unit at the time of rewriting.
WO2014/033851 discloses that “in a semiconductor device, when erasing data by using a band-to-band tunneling method, the supply of a boosted voltage to a memory cell to be erased is terminated if, in addition to the condition that the output voltage of a charge pump circuit has recovered to a predetermined criterion voltage, another condition is satisfied that a predetermined criterion time has elapsed from the start of supply of the boosted voltage to the memory cell to be erased.”